/* ec_dh.c - TinyCrypt implementation of EC-DH */

/*
 * Copyright (c) 2014, Kenneth MacKay
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 *  Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 *
 *    - Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *
 *    - Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 *    - Neither the name of Intel Corporation nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */
#include "ecc_dh.h"
#include <string.h>
#include "constants.h"
#include "ecc.h"
#include "utils.h"

#if default_RNG_defined
static uECC_RNG_Function g_rng_function = &default_CSPRNG;
#else
static uECC_RNG_Function g_rng_function = 0;
#endif

int uECC_make_key_with_d(uint8_t *public_key, uint8_t *private_key,
                         unsigned int *d, uECC_Curve curve) {
  uECC_word_t _private[NUM_ECC_WORDS];
  uECC_word_t _public[NUM_ECC_WORDS * 2];

  /* This function is designed for test purposes-only (such as validating NIST
   * test vectors) as it uses a provided value for d instead of generating
   * it uniformly at random. */
  memcpy(_private, d, NUM_ECC_BYTES);

  /* Computing public-key from private: */
  if (EccPoint_compute_public_key(_public, _private, curve)) {
    /* Converting buffers to correct bit order: */
    uECC_vli_nativeToBytes(private_key, BITS_TO_BYTES(curve->num_n_bits),
                           _private);
    uECC_vli_nativeToBytes(public_key, curve->num_bytes, _public);
    uECC_vli_nativeToBytes(public_key + curve->num_bytes, curve->num_bytes,
                           _public + curve->num_words);

    /* erasing temporary buffer used to store secret: */
    _set_secure(_private, 0, NUM_ECC_BYTES);

    return 1;
  }
  return 0;
}

int uECC_make_key(uint8_t *public_key, uint8_t *private_key, uECC_Curve curve) {
  uECC_word_t _random[NUM_ECC_WORDS * 2];
  uECC_word_t _private[NUM_ECC_WORDS];
  uECC_word_t _public[NUM_ECC_WORDS * 2];
  uECC_word_t tries;

  for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) {
    /* Generating _private uniformly at random: */
    uECC_RNG_Function rng_function = uECC_get_rng();
    if (!rng_function ||
        !rng_function((uint8_t *)_random, 2 * NUM_ECC_WORDS * uECC_WORD_SIZE)) {
      return 0;
    }

    /* computing modular reduction of _random (see FIPS 186.4 B.4.1): */
    uECC_vli_mmod(_private, _random, curve->n,
                  BITS_TO_WORDS(curve->num_n_bits));

    /* Computing public-key from private: */
    if (EccPoint_compute_public_key(_public, _private, curve)) {
      /* Converting buffers to correct bit order: */
      uECC_vli_nativeToBytes(private_key, BITS_TO_BYTES(curve->num_n_bits),
                             _private);
      uECC_vli_nativeToBytes(public_key, curve->num_bytes, _public);
      uECC_vli_nativeToBytes(public_key + curve->num_bytes, curve->num_bytes,
                             _public + curve->num_words);

      /* erasing temporary buffer that stored secret: */
      _set_secure(_private, 0, NUM_ECC_BYTES);

      return 1;
    }
  }
  return 0;
}

int uECC_shared_secret(const uint8_t *public_key, const uint8_t *private_key,
                       uint8_t *secret, uECC_Curve curve) {
  uECC_word_t _public[NUM_ECC_WORDS * 2];
  uECC_word_t _private[NUM_ECC_WORDS];

  uECC_word_t tmp[NUM_ECC_WORDS];
  uECC_word_t *p2[2] = {_private, tmp};
  uECC_word_t *initial_Z = 0;
  uECC_word_t carry;
  wordcount_t num_words = curve->num_words;
  wordcount_t num_bytes = curve->num_bytes;
  int r;

  /* Converting buffers to correct bit order: */
  uECC_vli_bytesToNative(_private, private_key,
                         BITS_TO_BYTES(curve->num_n_bits));
  uECC_vli_bytesToNative(_public, public_key, num_bytes);
  uECC_vli_bytesToNative(_public + num_words, public_key + num_bytes,
                         num_bytes);

  /* Regularize the bitcount for the private key so that attackers cannot use a
   * side channel attack to learn the number of leading zeros. */
  carry = regularize_k(_private, _private, tmp, curve);

  /* If an RNG function was specified, try to get a random initial Z value to
   * improve protection against side-channel attacks. */
  if (g_rng_function) {
    if (!uECC_generate_random_int(p2[carry], curve->p, num_words)) {
      r = 0;
      goto clear_and_out;
    }
    initial_Z = p2[carry];
  }

  EccPoint_mult(_public, _public, p2[!carry], initial_Z, curve->num_n_bits + 1,
                curve);

  uECC_vli_nativeToBytes(secret, num_bytes, _public);
  r = !EccPoint_isZero(_public, curve);

clear_and_out:
  /* erasing temporary buffer used to store secret: */
  _set_secure(p2, 0, sizeof(p2));
  _set_secure(tmp, 0, sizeof(tmp));
  _set_secure(_private, 0, sizeof(_private));

  return r;
}
